I would place Terrakion at A. Terrakion beats quite a lot of stuff in these very rankings, including the beast itself (Kanga), Zapdos, Charizard, Hydreigon, and many others. It can do this through amazing coverage in CC, Stone Edge, EQ, and a few more. Terra also has a very nice Speed tier, letting it outspeed a good but of the tier. However, something no one has brought up/many people don't use is Sash Terrakion. Sash Terra can beat a lot of stuff it otherwise loses to, such as Band Talon and Greninja. Another underated aspect is Quick Attack, which, as weird as it sounds, beats the many Focus Sash users in the tier. I wouldn't put it any higher because there is also stuff in these ranks that handles it, but I find myself bringing Terra quite a lot due to its ability to handle such a good bit of the metagame.
You may want to use some hide tags when posting a lot of calcs. ( )Lets do this:
Terrakion for A-, my reason is this, he covers both Mega Kangaskan and Aegislash, top tier threats.
Checks for Aegislash:
252+ SpA Aegislash-Blade Shadow Ball vs. 0 HP / 4 SpD Terrakion: 174-205 (53.8 - 63.4%) -- guaranteed 2HKO
252+ Atk Aegislash-Blade Shadow Sneak vs. 0 HP / 0 Def Terrakion: 88-105 (27.2 - 32.5%) -- guaranteed 4HKO
252+ Atk Aegislash-Blade Sacred Sword vs. 0 HP / 0 Def Terrakion: 262-310 (81.1 - 95.9%) -- guaranteed 2HKO
252 Atk Terrakion Earthquake vs. 252 HP / 0 Def Aegislash-Blade: 376-444 (116 - 137%) -- guaranteed OHKO
252 Atk Terrakion Earthquake vs. 252 HP / 0 Def Aegislash-Shield: 154-182 (47.5 - 56.1%) -- 25.8% chance to 2HKO after Leftovers recovery
He can plain on kill aegislash with just EG, and bulk doesn't really change the check much, just means aegi cant kill Terra even more
252 Atk Terrakion Earthquake vs. 252 HP / 252+ Def Aegislash-Shield: 118-140 (36.4 - 43.2%) -- 98.1% chance to 3HKO after Leftovers recovery
252 Atk Terrakion Earthquake vs. 252 HP / 252+ Def Aegislash-Blade: 236-278 (72.8 - 85.8%) -- guaranteed 2HKO after Leftovers recovery
4 SpA Aegislash-Blade Shadow Ball vs. 0 HP / 4 SpD Terrakion: 135-159 (41.7 - 49.2%) -- guaranteed 3HKO
4 Atk Aegislash-Blade Shadow Sneak vs. 0 HP / 0 Def Terrakion: 67-81 (20.7 - 25%) -- 0% chance to 4HKO
4 Atk Aegislash-Blade Sacred Sword vs. 0 HP / 0 Def Terrakion: 202-238 (62.5 - 73.6%) -- guaranteed 2HKO
Checks for Mega Kang:
252 Atk Parental Bond Mega Kangaskhan Sucker Punch vs. 0 HP / 0 Def Terrakion: 69-82 (21.3 - 25.3%) -- 0.2% chance to 4HKO
Plus Terra gets the +2 atk boost and even without the boost can will it with Close C
252 Atk Terrakion Close Combat vs. 0 HP / 4 Def Mega Kangaskhan: 390-458 (111.1 - 130.4%) -- guaranteed OHKO
252 Atk Parental Bond Mega Kangaskhan Earthquake vs. 0 HP / 0 Def Terrakion: 348-411 (107.7 - 127.2%) -- guaranteed OHKO
While it can OHKO Terra with EG, Terra can outspeed it even without C scarf (must be jolly/spd nature though)
252 Atk Parental Bond Mega Kangaskhan Fake Out vs. 0 HP / 0 Def Terrakion: 52-63 (16 - 19.5%) -- possible 6HKO
252 Atk Parental Bond Mega Kangaskhan Return vs. 0 HP / 0 Def Terrakion: 133-157 (41.1 - 48.6%) -- guaranteed 3HKO